Determining a target transmit power of a wireless transmission according to security requirements

ABSTRACT

Different target transmit powers are determined for different wireless transmissions from a wireless device, the different transmissions having different security requirements. For example, the security requirements of a particular transmission may include a security ranking of a device to which one or more frames carried by the particular transmission are addressed. In another example, the security requirements of a particular transmission may include the confidentiality of data carried by the particular transmission.

BACKGROUND OF THE INVENTION

In general, wireless communication is insecure and vulnerable toattacks. Various techniques may be employed to secure a wirelesscommunication link or to make it less vulnerable to attacks. Forexample, it is recommended to place a wireless access point away fromexternal walls and to lower the transmit power of its antenna so thatthe signal strength is strong enough for use inside the building butweak outside of the building where it may be accessible by others.

Bluetooth® wireless technology provides short-range and low powerwireless connectivity to eliminate the need for cables to connectcomputerized devices and their peripheral devices. A non-exhaustive listof examples of computerized devices includes personal computers (PCs),mobile phones, personal digital assistants (PDA), portable computers,pagers, handheld devices, and the like. A non-exhaustive list ofexamples of peripheral devices includes headsets, printers, keyboards,mice, and the like.

The Bluetooth® specifications were designed with various concepts inmind, including output power control that optimizes power according todevice distance. According to the Bluetooth® specification version 1.2,there are three classes of transmitters, and power control is mandatoryonly for those transmitters in the class where the maximum output poweris 100 mW (20 dBm) and the minimum output power at the maximum powersetting is 1 mW. At page 33 of the Radio Specification section of theBluetooth® specification version 1.2, it is stated “The power control(of a power class 1 device) is used for limiting the transmitted powerover +4 dBm. Power control capability under +4 dBm is optional and couldbe used for optimizing the power consumption and overall interferencelevel”.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereference numerals indicate corresponding, analogous or similarelements, and in which:

FIG. 1 is a schematic diagram of an exemplary system, according to someembodiments of the invention;

FIG. 2 is a flowchart of a method to be implemented by one of thedevices in FIG. 1, according to some embodiments of the invention; and.

FIG. 3 is a block diagram of one of the devices in the system of FIG. 1,according to some embodiments of the invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of embodiments of theinvention. However it will be understood by those of ordinary skill inthe art that the embodiments of the invention may be practiced withoutthese specific details. In other instances, well-known methods,procedures, components and circuits have not been described in detail soas not to obscure the embodiments of the invention.

FIG. 1 is a schematic diagram of an exemplary system, according to someembodiments of the invention. A system 100 includes a mobile device 102and one or more additional devices able to communicate with mobiledevice 102. For example, these other devices may include peripheralssuch as a wireless smart card reader 104, a wireless headset 106, and awireless printer 108, which may be able to communicate with device 102over wireless communication links 114, 116 and 118, respectively. Anon-exhaustive list of examples of wireless local area network standardsfor wireless communication links 114, 116 and 118 includes the Instituteof Electrical and Electronic Engineers (IEEE) for Wireless LAN MAC andPhysical layer (PHY) 802.11a, b, g and n specifications or futurerelated standards, the Bluetooth® standard, the Zigbee™ standard and thelike.

A smart card 103 is shown inserted into smart card reader 104. Smartcards are personalized security devices, defined by the ISO7816 standardand its derivatives, as published by the International Organization forStandardization. A smart card may have a form factor of a credit cardand may include a semiconductor device. The semiconductor device mayinclude a memory that can be programmed with a secret key and with anauthentication certificate, and may include a decryption engine, e.g., aprocessor and/or dedicated decryption logic. A smart card may include aconnector for powering the semiconductor device and performing serialcommunication with an external device. Alternatively, smart cardfunctionality may be embedded in a device having a different form factorand different communication protocol, for example a Universal Serial Bus(USB) device. The person whose security information is stored on smartcard 103 may use smart card reader 104 for identification and todigitally sign and/or decrypt messages sent by device 102.

For example, mobile device 102 may be able to send and receive e-mailmessages via an e-mail server (not shown). If, for example, the SecureMultipurpose Internet Mail Extensions (S/MIME) protocol is used, e-mailmessages received at mobile device 102 are encrypted using a symmetricalgorithm with a random session key generated by the sender of thee-mail message. The e-mail message also includes the session key,encrypted using the public key of the recipient. Upon receipt of anencrypted e-mail message, mobile device 102 may extract the encryptedsession key and send it to smart card reader 104 via communication link114. Smart card reader 104 may send the encrypted session key to smartcard 103, and the decryption engine of smart card 103 may decrypt theencrypted session key using the recipient's private decryption key,which is stored in smart card 103. Smart card reader 104 may retrievethe decrypted session key from smart card 103 and forward it to mobiledevice 102 via communication link 114 so that mobile device 102 candecrypt the received e-mail message. The smart card 103 may preventunauthorized use of the recipient's private decryption key by requiringthat a password or personal identification number (PIN) be suppliedbefore allowing the decryption operation to proceed.

Similarly, to add a digital signature to an e-mail message being sent bymobile device 102, mobile device 102 may send a hash of the contents ofthe e-mail message to smart card reader 104 over communication link 114.Smart card reader 104 may pass the hash to smart card 103, which mayproduce a digital signature from the hash and the sender's privatesigning key, which is stored in smart card 103. Smart card 103 may thenpass the digital signature to smart card reader 104, which may forwardit to mobile device 102 via communication link 114 so that mobile device102 can transmit it along with the e-mail message to the e-mail server.Again, smart card 103 may prevent unauthorized use of the recipient'sprivate signing key by requiring that a password or PIN be suppliedbefore allowing the signing operation to proceed.

The unencrypted session key should be sent securely over communicationlink 114 from smart card reader 104 to mobile device 102 to prevent athird party from retrieving the session key from communication link 114.Similarly, the hash to be signed should be sent authentically overcommunication link 114 from smart card reader 104 to mobile device 102to prevent a third party from modifying the hash and thereby causingsmart card 103 to produce a signature using a hash different from thehash of the intended message. Smart card reader 104 and mobile device102 may each store a common, symmetric key and use a symmetric algorithmto secure communications over communication link 114. Alternatively,smart card reader 104 and mobile device 102 may store their own privatekeys and each other's public keys, and use an asymmetric algorithm tosecure communications over communication link 114.

Headset 106 may communicate with mobile device 102 over wirelesscommunication link 116 and may extend audio functionality of mobiledevice 102. For example, mobile device 102 may include cellphonefunctionality, and headset 106 may provide mobile device 102 with audioinput and output functions, enabling a user to listen to voice mail,handle voice calls and issue voice commands to mobile device 102. Inanother example, mobile device 102 may include audio playbackfunctionality, for example an MP3 (moving picture experts group layer 3audio) playback functionality, and headset 106 may provide device 102with an audio output function, enabling a user to listen to audioplayback.

Mobile device 102 may include data functionality, for example, e-mailfunctionality. Mobile device 102 may be able to send data over wirelesscommunication link 118 to be printed by wireless printer 108.

Wireless communication links 114, 116 and 118 may be vulnerable toeavesdropping. However, mobile device 102 may be close physically to oneor more of devices 104, 106 and even 108. Thus, device 102 may be ableto communicate with devices that are nearby at lower powers than withdevices that are farther away.

FIG. 2 is a flowchart of a method to be implemented by one or more ofdevices 102, 104 and 106, according to some embodiments of theinvention. At 202, one or more of devices 102, 104 and 106 may determinedifferent target transmit powers for different wireless transmissionshaving different security requirements. The stricter the securityrequirements, the lower the target transmit power, so that sensitivetransmissions are “whispered” and therefore less vulnerable toeavesdropping. The actual transmit power of a wireless transmission,measured at the antenna of the transmitting device, may differ from thetarget transmit power due to various factors.

The security requirements of a particular transmission may include apredetermined or dynamically determined security ranking of the deviceto which one or more frames carried by the particular transmission areaddressed, with a lower target transmit power for transmissions carryingframes addressed to devices at higher security rankings than fortransmission carrying frames addressed to devices at lower securityrankings.

For example, since communications between mobile device 102 and smartcard reader 104 may be generally more confidential than communicationsbetween mobile device 102 and headset 106, mobile device 102 maydetermine a lower target transmit power for transmissions intended forsmart card reader 104 than for transmissions intended for headset 106.However, the security ranking of a device may be dependent on otherfactors. For example, the security ranking of smart card reader 104 maybe lower while the user is at an authorized workplace than while theuser is located outside the authorized workplace. At the authorizedworkplace, mobile device 102 may determine a relatively high targettransmit power for transmissions intended for smart card reader 104 soas to avoid retries due to lack of reception by smart card reader 104 ofthose transmissions.

In another example, if the sender of a transmission recognizes thatthere are other transmitters in the area (for example, other activeBluetooth® radios), the sender may reduce the target transmit power ofthe transmission to make it harder for the other transmitters to receivethe transmission. This is analogous to “whispering” when someone isstanding nearby.

The security requirements of a particular transmission may include theconfidentiality of data carried by the particular transmission, withlower target transmit powers for transmissions carrying data of higherconfidentiality than for transmissions carrying data of lowerconfidentiality.

For example, telephone calls with members of the user's family may beconsidered less confidential than telephone calls with the user'sco-workers. Accordingly, the target transmission power for transmissionsbetween mobile device 102 and headset 106 may be lower for sometelephone calls than for others.

In another example, documents may have different confidentialityrankings. The target transmission power for transmitting documents frommobile device 102 to printer 108 may vary according to theconfidentiality ranking of the document.

In yet another example, as explained hereinabove, to add a digitalsignature to an e-mail message being sent by mobile device 102, mobiledevice 102 may send a hash of the contents of the e-mail message tosmart card reader 104. Smart card reader 104 may pass the hash to smartcard 103, which may produce a digital signature from the hash and thesender's private signing key, which is stored in smart card 103. Smartcard 103 may prevent unauthorized use of the recipient's private signingkey by requiring that a password or PIN be supplied before allowing thesigning operation to proceed. Since the password or PIN is moreconfidential than the hash of the contents of the e-mail message, mobiledevice 102 may determine a lower target transmit power for thetransmission carrying the password or PIN than for the transmissioncarrying the hash of the contents of the e-mail message.

If mobile device 102 does not detect a valid response from the devicefor which the transmission is intended (checked at 204), mobile device102 may act according to a security policy. For example, at 206, mobiledevice 102 may prompt the user to bring mobile device 102 and the devicefor which the transmission is intended closer together. In anotherexample, at 208, mobile device 102 may increase the target transmitpower for transmissions intended for that device, possibly subject to anupper limit.

FIG. 3 is a block diagram of a device 300, according to some embodimentsof the invention. Device 300 may be, for example, mobile device 102,smart card reader 104, or headset 106. For clarity, some components ofdevice 300 are not shown in FIG. 3 and are not described explicitlybelow.

Device 300 includes an antenna 302. A non-exhaustive list of examplesfor antenna 302 includes a dipole antenna, a monopole antenna, amultilayer ceramic antenna, a planar inverted-F antenna, a loop antenna,a shot antenna, a dual antenna, an omnidirectional antenna and any othersuitable antenna.

Device 300 also includes a wireless transceiver 304 including a radio303 coupled to antenna 302. Wireless transceiver 304 includes bothtransmitter and receiver functionality. A non-exhaustive list ofexamples for standards with which wireless transceiver 304 may becompatible includes 802.11a, b, g and n and future related standards,the Bluetooth® standard, the Zigbee™ standard and the like.

Device 300 also includes a processor 306 coupled to transceiver 304.Device 300 also includes a memory 308, which may be fixed in orremovable from device 300. Memory 308 may be coupled to processor 306 orpartly embedded in processor 306. Transceiver 304 and processor 306 maybe part of the same integrated circuit or in separate integratedcircuits. Similarly, processor 306 and memory 308 may be part of thesame integrated circuit or in separate integrated circuits.

A non-exhaustive list of examples for processor 306 includes a centralprocessing unit (CPU), a digital signal processor (DSP), a reducedinstruction set computer (RISC), a complex instruction set computer(CISC) and the like. Furthermore, processor 306 may be part of anapplication specific integrated circuit (ASIC) or may be a part of anapplication specific standard product (ASSP).

A non-exhaustive list of examples for memory 308 includes anycombination of the following:

a) semiconductor devices such as registers, latches, read only memory(ROM), mask ROM, electrically erasable programmable read only memorydevices (EEPROM), flash memory devices, non-volatile random accessmemory devices (NVRAM), synchronous dynamic random access memory (SDRAM)devices, RAMBUS dynamic random access memory (RDRAM) devices, doubledata rate (DDR) memory devices, static random access memory (SRAM),universal serial bus (USB) removable memory, and the like;

b) optical devices, such as compact disk read only memory (CD ROM), andthe like; and

c) magnetic devices, such as a hard disk, a floppy disk, a magnetictape, and the like.

Memory 308 may store executable code 310 which, when executed byprocessor 306, determines different target transmit powers for differenttransmissions to be transmitted by transceiver 306 and having differentsecurity requirements.

Executable code 310, when executed by processor 306, may cause device300 to implement the method of FIG. 2.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the spirit ofthe invention.

1. A device comprising: a processor; a memory to store executable code which, when executed by said processor, determines a target transmit power for a wireless transmission based, at least in part, on a security ranking of a device to which one or more frames carried by said wireless transmission are addressed; and a wireless transmitter to transmit said wireless transmission.
 2. The device of claim 1, wherein said target transmit power is lower for a wireless transmission carrying one or more frames addressed to a device having a higher security ranking than for a wireless transmission carrying one or more frames addressed to a device having a lower security ranking.
 3. The device of claim 1, wherein said device is a mobile device.
 4. The device of claim 1, wherein said device includes smart card reader functionality.
 5. The device of claim 1, wherein said device is a headset.
 6. The device of claim 1, wherein said wireless transmitter is compatible with a Bluetooth standard.
 7. A device comprising: a processor; a memory to store executable code which, when executed by said processor, determines a target transmit power for a wireless transmission the based, at least in part, on confidentiality of encrypted data carried by said wireless transmission; and a wireless transmitter to transmit said wireless transmission.
 8. The device of claim 7, wherein said target transmit power is lower for a wireless transmission carrying encrypted data of higher confidentiality than for a wireless transmission carrying encrypted data of lower confidentiality.
 9. The device of 7, wherein said device is a mobile device.
 10. The device of claim 7, wherein said device includes smart card reader functionality.
 11. The device of claim 7, wherein said device is a headset.
 12. The device of claim 7, wherein said wireless transmitter is compatible with a Bluetooth standard.
 13. A device comprising: a processor; a memory to store executable code which, when executed by said processor, determines different target transmit powers for different wireless transmissions having different security requirements; a wireless transmitter to transmit said different wireless transmissions; and a wireless receiver, wherein said executable code, when executed by said processor, increases a target transmit power for a particular wireless transmission in the absence of receipt of a valid response by said wireless receiver from a device for which said particular wireless transmission is intended.
 14. The device of claim 13, wherein said device is a mobile device.
 15. The device of claim 13, wherein said device includes smart card reader functionality.
 16. The device of claim 13, wherein said device is a headset.
 17. The device of claim 13, wherein said wireless transmitter is compatible with a Bluetooth standard.
 18. A method in a wireless-enabled device, the method comprising: determining a target transmit power of a wireless transmission based, at least in part, on a security ranking of a device to which one or more frames carried by said wireless transmission are addressed; and transmitting said wireless transmission.
 19. The method of claim 18, wherein determining said target transmit power of said wireless transmission includes determining a lower target transmit power for a wireless transmission carrying one or more frames addressed to a device having a higher security ranking than for a wireless transmission carrying one or more frames addressed to a device having a lower security ranking.
 20. A method in a wireless-enabled device, the method comprising: determining a target transmit power of a wireless transmission based, at least in part, on confidentiality of encrypted data carried by said wireless transmission; and transmitting said wireless transmission.
 21. The method of claim 20, wherein determining said target transmit power of said wireless transmission includes determining a lower target transmit power for a wireless transmission carrying encrypted data of higher confidentiality than for a wireless transmission carrying encrypted data of lower confidentiality.
 22. A method in a wireless-enabled device, the method comprising: determining different target transmit powers for different wireless transmissions having different security requirements; transmitting said different wireless transmissions; and increasing a target transmit power of a particular wireless transmission in the absence of a valid response from a device for which said particular wireless transmission is intended. 